Gas phase polyethylene copolymers

Abstract

Polyethylene copolymers with a structure that provides improved film properties are provided. The copolymers can have a density of about 0.905 to about 0.911 g/cm 3 . The copolymers can also have a DRI/I2 ratio of about 0.0008 to about 0.060, an I2 value of about 0.6 to about 3.8 dg/min, and an I21 value of about 8 to about 57 dg/min. The copolymers having those properties can be produced by introducing ethylene and at least one other olefin comonomer to a single reactor at a comonomer/ethylene mole ratio of about 0.02 to about 0.03 and polymerizing at a temperature of about 76.7° C. to about 80.6° C. and a pressure of about 1,724 kPa to about 2,413 kPa. The copolymers can be used to make films having a 21 mol % O 2 transmission rate of about 150 to about 200 cc/100 in 2 /24 hr. and hot tack seal initiation temperatures of about 65° C. to 80° C.

What is claimed is: 
     
       1. An ethylene copolymer, comprising:
 about 92.5 mol % to about 97.5 mol % ethylene derived units; and 
 about 2.5 mol % to about 7.5 mol % hexene-derived units, 
 wherein the copolymer has
 a density of about 0.905 g/cm 3  to about 0.911 g/cm 3 ; 
 a first Melt Index (I2) of about 0.4 to about 3.4 dg/min, as measured according to ASTM D138(190° C./2.16 kg); 
 a second Melt Index (I21) of about 5 to about 60 dg/min, as measured according to ASTM D138 (190° C./21.6 kg); 
 a Melt flow ratio (I21/I2) of about 16 to about 17; and 
 a Dow Rheology Index (DRI)/Melt Index (I2) ratio (DRI/I2) of about 0.007 to about 0.060; 
 
 wherein the copolymer is produced by
 introducing the ethylene and the 1-hexene to a single gas phase reactor at a 1-hexene/ethylene mole ratio of about 0.02 to about 0.03, as determined by measuring moles of the 1-hexene and the ethylene in a vapor overhead of the single reactor; and 
 polymerizing the ethylene and the 1-hexene at a temperature of about 75.56° C. to about 80° C. and a pressure of from 290.0 psig to 299.7 psig. 
 
 
     
     
       2. The copolymer of  claim 1 , further having a density of about 0.907 g/cm 3  to about 0.911 g/cm 3 . 
     
     
       3. The copolymer of  claim 2 , having one or both of the following properties:
 (a-1) a density of about 0.908 g/cm 3  to about 0.910 g/cm 3 ; and 
 (b-1) a DRI/I2 ratio of about 0.007 to about 0.028. 
 
     
     
       4. A film made from the copolymer of  claim 1 , the film having:
 (a) a thickness of about 1 mil; 
 (b) a 21 mol % oxygen transmission rate of about 150 to about 200 cc/100 in 2 /24 hr; and 
 (c) a hot tack seal initiation temperature of about 65° C. to about 80° C. 
 
     
     
       5. The film of  claim 4 , having one or both of the following properties:
 (b-1) the 21 mol % oxygen transmission rate of 160 to 200 cc/100 in 2 2/24 hr; and 
 (c-1) the hot tack seal initiation temperature of 67° C. to 78° C. 
 
     
     
       6. The film of  claim 5 , having one or both of the following properties:
 (b-2) the 21 mol % oxygen transmission rate of 170 to 190 cc/100 in 2 /24 hr; and 
 (c-2) the hot tack seal initiation temperature of 70° C. to 75° C.